1. Field of the Invention
This invention relates to a method of forming a photographic image by intensification using a halogenite, hydrogen peroxide or a compound capable of releasing hydrogen peroxide, more particularly, to a method of forming a photographic image while inhibiting fog by effecting image intensification in the presence of a nitro-substituted nitrogen-containing heterocyclic compound.
2. Description of the Prior Art
It is known that a photographic light-sensitive material using a light-sensitive metal salt can be exposed, subjected to chemical or physical development to form a catalytically active metallic image of a Group VIII, VI a or I b metal and a color image or a tanning image is oxidizingly formed in a photographic element in the presence of hydrogen peroxide or a compound capable of releasing hydrogen peroxide with a reducing agent or a reducing agent and color forming agent, as disclosed in West German Patent Applications (OLS) 1,813,920, 1,950,102, 1,995,901, 1,961,029, 2,044,833, 2,044,993, 2,056,360, 2,056,359 and 2,120,091 and Japanese Patent Applications 128,327/1974 and 139,917/1974.
In the field of color photography, with which the present invention deals, a color photographic material prepared by incorporating color formers such as cyan, yellow and magenta in a silver halide photographic emulsion by various methods and applying the emulsion to a support is subjected to image-wise exposure and then to a series of processings to reproduce the image on the photographic material.
The basic processings involved are color development processing and silver removal processing. A silver halide color photographic material is exposed and then developed with a color developing agent in the color developing processing. That is to say, the silver halide is reduced by the color developing agent to form a silver image while the color developing agent thus oxidized is reacted with the color former to give a color image. Then, the color photographic material undergoes silver removal processing, wherein the silver formed is oxidized by the action of an oxidizing agent generally called a "bleaching agent", dissolved by a complexing agent for silver ions generally called a "fixing agent" and removed from the photographic material. Thus, only the color image remains. In practical development, the above described basic processings of color development and silver removal are further accompanied by other auxiliary processings to retain the photographic and physical qualities of an image or to improve the storage capability of an image, for example, by hardening to prevent the light-sensitive film from excess softening during processing, stopping to effectively stop the development reaction, stabilizing to stabilize the image or a film removal to remove a backing layer from the support.
Since 1940, color photographic processing of this kind has commonly been carried out. A color light-sensitive material used in such color processing contains about 1 to 15 g of silver per 1 m.sup.2 of the sensitive material in the form of a silver halide. For example, many reflection image materials (typical of which are color papers) contain 1 to 2.5 g of silver per 1 m.sup.2 of the sensitive material, and many photographing materials such as color negative films and color reversal films contain 3 to 9 g of silver per 1 m.sup.2. This quantity of silver is necessary to obtain a desirable color image density, but it is preferred to reduce the quantity of silver from the standpoint of saving silver source as well as reducing production costs.
U.S. Pat. No. 3,674,490 describes a method whereby the quantity of a silver halide in a light-sensitive material can be reduced by a color intensification. According to this specification, an image-wise distributed metallic image acts as a catalyst to activate a peroxide such as hydrogen peroxide and an oxidation reaction is thus carried out to form a dye and a color image. Since such a metallic image is present as a catalyst, the quantity thereof may be very small. In the case where the metal image is silver, therefore, a desirable color density can be provided with a lessened quantity of silver salt than the quantity of silver salt used in a gelatino-silver salt emulsion of the prior art. In this method, a peroxide is used in an intensification step after the development, that is, color development. However, this method has many disadvantages, for example, a peroxide such as hydrogen peroxide is very unstable in aqueous solution. Stabilization of aqueous hydrogen peroxide can be accomplished by the addition of sodium pyrophosphate or sodium stannate as a stabilizer as described in "Research Disclosure" 11660 or W. C. Schumb: "Hydrogen Peroxide" page 515-547. Furthermore, marked fog occurs due to intensification.